Want perfectly color corrected photos? Stick a translucent white disc in front of your camera lens for one test photo and the rest of your pictures taken in odd lighting situations will have the same neutral color cast your eyes saw when you shot the picture. Correct color balance is the promise and delivery of the Expo Imaging ExpoDisc. It works this way: Set your camera for auto exposure, take one picture with the calibrated ExpoDisc filter in front of your lens, remove the ExpoDisc, then tell the camera to use that photo to set white balance. The photo above shows an image taken under incandescent light using auto white balance (left) and corrected with an ExpoDisc (right); the background in real life is off white, as the right picture captures. Of all the methods I've tried, ExpoDisc works best and is most idiot-proof. As well it should be, for the ExpoDiscs run $60 to $105 (direct) depending on lens diameter. Just buy whatever fits your largest lens and let it overlap the others. ExpoDisc isn't cheap if you're a casual photographer, but it does work in almost every lighting situation.

As Geoff Fox explained in his white balance primer, there is a color temperature associated with each type of lighting: sunlight, open shade that makes objects appear slightly blue, incandescent light bulbs that make objects appear brownish (see the photo above), and florescent bulbs that give an image a greenish cast. Your camera's auto white balance setting does the job partly but seldom perfectly. Your options include living with the image (the most popular choice), dialing in a color correction on your DSLR and some advanced pocket cameras (indoor lighting, shade, fluorescents), or in photo editing software trying to pick a neutral white or gray spot (which sometimes makes the image look worse when it turns out the spot isn't a neutral color after all). If you shoot in RAW format, it's easier to correct off colors (RAW applies no camera corrections) but RAW images suck up huge amounts of space, sometimes 20MB per image. One solution is to shoot in RAW and JPG both, and keep only the RAW images of the most important photos. That's easier said than done since you've got to find the time to decide which photos are the ones you want to keep; in the meantime you can be sucking down 1 GB of disk space for every 50-100 photos. I have some five-year-old RAW images I've been meaning to cull - someday soon.

In working with the ExpoDisc filter I found the color correction to be spot-on. So much so that what's actually corrected to neutral seemed a bit cool. Thus there's also an ExpoDisc Portrait filter that warms the image ever so slightly and I prefer that for portraits. But all of a sudden you're talking $120 to $210 to get both. Ka-ching. For a pro whose reputation depends on great photos, it's a cost of doing business. For others, just get one; then you can try tweaking the color temperature ever so slightly in your image editing software. ExpoImaging says the difference between the normal and portrait filters is the same as putting a Wratten 81A warming filter in front of the lens. If you've got Adobe Photoshop, that's actually an effect you can add with one click.

In working with ExpoDisc, I found:

--The method for setting white balance varies from camera to camera, even within one brand. Study the online instructions before heading out to shoot photos the first time.

-- You don't leave the ExpoDisc on for the actual pictures after the first test photo. The filter transmits light but not the image. The filter looks a bit like the diamond-shaped diffuser in a fluorescent light. It comes with a neck lanyard as well as a protective carry case.

-- For best results, take the test photo from where the subject is, aiming back at where the camera will shoot from, because there may be a slight variation in color temperature, more so indoors that out.

-- ExpoDisc transmits 18% of the light, which is what most scenes average out to be. That helps you set exposure for tricky conditions such as shooting sports against a backdrop of dark trees, which leads to overexposed photos. Here's why: When a camera sees a dark background, the camera sees it as a normal not dark background that's getting insufficient light, so it boosts the exposure and that washes out the photo.

-- ExpoDisc won't work in many arenas and rinks because the color temperatures and even the light output of some sodium vapor and mercury vapor lamps actually fluctuate multiple times per second.

-- If ExpoDisc is too rich for your blood, Expo Imaging makes a less costly ExpoCap that provides basic white balance correction for $45-$60 direct. It should be good enough for many users. You can't use ExpoCap to help determine exposure.